1. Field of the Invention
The invention relates to the packaging and interconnection of microwave integrated circuits or monolithic microwave integrated circuits with a waveguide structure. (As used herein microwave integrated circuit will be taken generically to mean both microwave integrated circuits and monolithic microwave integrated circuits.) At both the transmit and receive ends of a microwave communications or radar system, energy radiators in the form of horns or slots are provided. It is necessary to transfer energy efficiently between microwave integrated circuits and these radiators. In order to achieve efficient energy transfer, it is necessary to transform the waveguide impedance and mode of propagation to that of the microwave integrated circuits and vice versa.
2. Description of the Prior Art
The prior art describes two techniques for providing impedance matching and mode conversion to effect energy transition between a microwave integrated circuit and a waveguide.
A first technique uses a coaxial connector element between a waveguide and a microwave integrated circuit. This technique has the disadvantages of relatively large size and weight, narrow bandwidth and considerable insertion losses of the circuit, especially at high frequencies. Consequently, it is of little or no use for certain applications such as direct broadcast satellite transmission.
The second technique uses a ridged waveguide transformer inserted in the waveguide between a full height section of the waveguide and the microwave integrated circuit. This technique has the disadvantage of using a device requiring highly complex and precise machining steps during fabrication. In addition, positioning the transformer in the waveguide requires difficult assembly procedures.
The introduction of monolithic microwave integrated circuits (MMIC's) has caused several additional problems directly related to their small size and fragility. With microstrip, it is possible to contact the substrate with a coaxial center conductor or a flat metal tab. Establishing a reliable contact is very difficult, if not impossible, with an MMIC circuit due to its fragility. Consequently, it is necessary to package MMIC's in a way which maximizes performance and reliability and minimizes size and weight.